1. Technical Field
This invention relates to special effects involving image signals and, more particularly, to image signal special effects such as those commonly viewable in the field of television.
2. Description of Related Art
In recent years, special effects on image signals have become an important part of television programming. The special effects commonly provide sequences of distortion or warping of an input video image on a field-by-field or frame-by-frame basis to produce an output video image. Initially, special effects were limited to operations such as zooming, translation and skewing.
A significant advancement was made with the advent of three-dimensional perspective transformations including three-dimensional perspective rotation as taught by three related U.S. Pat. No. 4,468,688 to Gabriel et al.; U.S. Pat. No. 4,631,750 to Gabriel et al. and U.S. Pat. No. 4,472,732 to Bennett et al., all of which are hereby incorporated by reference. U.S. Pat. No. 4,472,732 to Bennett discloses the use of a special effects processor to process both a video image and a key image. Improvements in such systems have continued with the development of recent products such as the ADO.RTM. 100 and the ADO.RTM. 500 special effects processors marketed by Ampex Corporation.
Systems have been developed to generate object surfaces to which input images can be applied or mapped in order to generate a desired output image. U.S. Pat. No. 4,791,581 to Ohba describes a method of designing surfaces for special effects. However, the computations for surface definition are extensive and the system does not readily lend itself to the mapping of entire video images onto the created surfaces. The Ohba system uses recurrence formulae, which have no simple inverse formulation that permits an inverse mapping between the surface and the planar images to enable control over distances on the surface between interpolation points.
U.S. Pat. No. 4,563,703 to Taylor et al. teaches a system that provides both spatial and temporal address interpolation. The '703 system requires preprogrammed shapes that are not operator controllable. Because of use of a direct mapping between input and output video images, the '703 system often uses greater or lesser numbers of address transformations than may be optimally required for an image.
The fundamental mathematics underlying geometric transformations such as video special effects are taught by references such as M. E. Mortenson, Geometric Modeling, John Wiley & Sons (1985) and I. D. Faux and M. J. Pratt, Computational Geometry for Design and Manufacture, Ellis and Harwood, Ltd. (1987). These two references are hereby incorporated by reference.
As special effects processors have become increasingly sophisticated, the control of the special effects has become increasingly complicated. Either the effects must be preprogrammed or an extremely complicated sequence of operator interaction is required to define a special effect. A need therefore exists for systems and methods that will produce sophisticated special effects that can be developed through an interactive operator interface with a reasonable level of complexity. Such a system and method ought to allow development of sophisticated special effects with a minimal number of operator commands and the operator commands should have predictable results. Construction of an effect becomes inordinately difficult if a large number of tedious commands are required or if it is difficult to predict the effect of a given operator command on a transformation that is being developed.